This mushroom is also known as portabella. When cremini mushrooms are left to grow larger, they turn into portobellos. Cultivation of portobellos has flourished in recent years and their price is coming down as supply increases. In a way, they are an inexpensive substitute for porcini mushrooms. They have a deep, meaty flavor and texture. The stems are tough and woody, often removed and added to soups and stock for flavor, but you can also slice and saute them. The large caps are the real draw in portobellos. They are wonderful for grilling or broiling whole. They can also become "burgers" or a mushroom "pizza" crust when topped with tomato and cheese, then baked. When thinly sliced, the caps make a pretty arrangement over traditional pizza. If using in light sauces, scrape out the dark gills from the undersides of the caps to avoid darkening the sauce.